RFID tags of conventional design cooperate with a reader to identify their presence in response to a signal having prescribed characteristics. In a typical RFID system, transponders (commonly referred to as “tags”) are attached to objects. Each tag can carry with it any imaginable data such as a serial or model number, a date of manufacture, or a country of origin or assembly. When these tags pass through a field generated by a compatible reader, they transmit or reflect signals back to the reader, thereby identifying the object. A multiplicity of tags can be manufactured and applied to products so as to uniquely identify a corresponding number of products. An exemplary application of RFIDs tags is to replace or supplement traditional bar codes that are disposed on products. One future benefit that has been mentioned in the press is that products in a shopping cart can be sensed in parallel and purchases tallied simply by moving the cart proximate to a reader, instead of requiring the products in the cart to have their bar codes scanned in a serial manner.
The ability of an RFID tag to be read from a distance has numerous other applications. For instance, there are circumstances in which it is desirable to include an RFID tag on a product in order to authenticate the item. For example, RFID tags can be included on prescription medication containers so that genuine pharmaceuticals can be distinguished from grey market or black market drugs. Likewise, authenticating tags can be included in premium consumer products such as handbags to differentiate genuine articles from imitations.
However, there are also circumstances in which it would be useful to include an RFID tag which would be non-transmissive (that is, would not provide a response to a reader) until the product package is opened. For example, it would be desirable to include an RFID tag in a collectable item (e.g., a baseball card) which can readily authenticate the item as a genuine collectable, yet which does not reveal the contents of the package until the item's packaging has been opened. There are also circumstances in which it would be beneficial to have the response state of an RFID tag conditioned on the position of a latch or other mechanical element. For example, if a window latch were to include an RFID tag that passively announces whether the window is in a locked or unlocked state, then home security could be improved. The present invention addresses these and other needs.